1. Field of the Invention
The present invention relates to a method of measuring a current density distribution of a beam of charged particles at an arbitary position on Z-coordinate in a workpiece, a method of adjusting the current density distribution, and a method of irradiating the workpiece while the beam of charged particles conducts scanning by a preferable scanning electric waveform in a hybrid scanning type apparatus such as an ion-implantation apparatus, an ion beam irradiation apparatus and an electron beam irradiation apparatus in which electromagnetic scanning of a beam of charged particles such as a ion beams, and mechanical drive of a workpiece such as a semiconductor board are jointly used.
2. Description of the Related Art
As a typical example of the above apparatus in which a beam of charged particles is used, there is provided an ion-implantation apparatus in which a workpiece is irradiated with an ion beams so that the ions can be implanted. In the following explanations, the ion-implantation apparatus is taken up as an example.
FIG. 7 is a schematic drawing showing a main portion of a conventional example of the hybrid scanning type ion-implantation apparatus. This apparatus is composed as follows. A workpiece (for example, a semiconductor board) 4 held by a holder 6 is mechanically reciprocated as shown by arrow A along one axis, which is Y-axis in this case, in the three dimensional space. Simultaneously, an ion beam 2, which proceeds along Z-axis substantially perpendicular to Y-axis, is electromagnetically subjected to scanning by a scanner not shown in the direction x substantially perpendicular to Y-axis and Z-axis, that is a ion beam 2 is subjected to scanning by an electric field and/or magnetic field, so that the workpiece 4 can be irradiated with the ion beam 2. Accordingly, it is possible to implant a desired dopant (impurities to be implanted) in a desired region (typically, all over the surface) of the workpiece 4 by a desired distribution (typically, uniformly). Reference numeral 8 designates a drive shaft for driving the holder 6.
In order to make the dopant exist in the desired region of the workpiece 4 by the desired distribution, it is necessary to control the mechanical drive of the workpiece 4 and the electromagnetic scanning of the ion beam 2 so that the desired distribution can be obtained. That is, in order to obtain the desired distribution in the direction of Y-axis, it is necessary to appropriately control the drive of the workpiece 4. Further, in order to obtain the desired distribution in the direction of X-axis, it is necessary to appropriately control the scanning of the ion beam 2. The present invention relates to the latter, that is, the present invention relates to the scanning of the ion beams.
In order to obtain the desired distribution of the dopant in the scanning direction of the ion beam 2 (the direction of X-axis), as well known, it is necessary to make a distribution of current density in the scanning direction of the ion beam 2 at a position where the ion beam 2 is incident upon the workpiece 4 coincide with the desired distribution of the dopant.
Therefore, conventionally, Faraday (current detector) 10, which is mechanically driven in the scanning direction of the ion beam 2, is arranged at a position of the workpiece 4 or in the proximity of the workpiece 4, and while Faraday 10 is driven as described above as shown by arrow B, a beam current is measured. Thus, a distribution of beam current density can be measured at the position. A scanner of the ion beam 2 is controlled by the measured data so that the distribution of beam current density at the position can be formed into a desired shape. This technique is disclosed, for example, in Toku Hyo Sho No. 64-500310.
In the above ion-implantation apparatus, in any case, as illustrated in FIG. 8, when the workpiece 4 is mechanically driven, the holder 6 is inclined, so that a tilt angle .theta., which is an angle formed between a surface of the workpiece 4 and Y-axis (in this case, the holder drive shaft 8), can be a constant value more than 0.degree.. This tilt angle .theta. is the same as the incident angle of the ion beam 2 which is incident upon the surface of the workpiece 4. The reason why the tilt angle .theta. is set at a value more than 0.degree. is to prevent the channeling effect of the ion beams with respect to a semiconductor board. Another reason why the tilt angle .theta. is set at a value more than 0.degree. is that ions are also implanted onto side walls of the trench structure formed on the surface of the workpiece.
When the tilt angle .theta. is increased as shown in FIG. 8, position Z.sub.1, on Z-coordinate at which the ion beam 2 subjected to scanning in X-direction is incident upon a lower end portion of the workpiece 4 in Y-direction and position Z.sub.3 on Z-coordinate at which the ion beam 2 subjected to scanning in X-direction is incident upon an upper end portion of the workpiece 4 in Y-direction are greatly different from position Z.sub.2 on Z-coordinate at the center of the workpiece 4. This tendency becomes more remarkable when a plane size of the workpiece 4 is increased.
In general, the ion beam 2, which has been electromagnetically subjected to scanning, is a group of ions, the proceeding directions of which are different a little from each other. Therefore, a distribution of beam current density in the scanning direction generally depends upon a position on Z-coordinate.
However, according to the conventional art described before, the distribution of current density of the ion beam 2 can be measured only at one point on Z-coordinate axis on which Faraday 10 is arranged, for example, the distribution of current density of the ion beam 2 can be measured only at position Z.sub.2 on Z-coordinate. Accordingly, distributions of current density at an upper and a lower portion of the workpiece 4 are different from the distribution measured by Faraday 10. As a result, the distributions of the dopant at the upper and the lower portion of the workpiece are. different from a desired distribution.
For example, in order to conduct ion-implantation uniformly all over the surface of the workpiece 4, when a beam scanner is controlled so that a distribution of beam current density in X-direction (scanning direction) can be uniform at position Z.sub.2 on Z-coordinate, a shape of the distribution of beam current density at position Z.sub.1, on Z-coordinate usually protrudes downward, and a shape of the distribution of beam current density at position Z.sub.3 on Z-coordinate usually protrudes upward. As a result, as shown in FIG. 10, the distribution becomes non-uniform in such a manner that a quantity of implanted dopant on the surface of the workpiece 4 at the center in the direction of X-axis is increased in the proximity of the upper portion of the workpiece 4, and a quantity of implanted dopant on the surface of the workpiece 4 at the center in the direction of X-axis is decreased in the proximity of the lower portion of the workpiece 4. In FIG. 10, the quantity of implanted dopant is increased in the order of marks of ---, --, -, +, ++, +++.